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Abstract:

A printer has a separating unit, such as a depressing cam and a
depressing slider, which presses a middle plate against the biasing force
of a spring and separates a sheet on the middle plate from a sheet
feeding roller by a predetermined distance, a separation driving unit,
such as a DC motor, which moves the separating unit, a measuring unit
which measures the driving load applied to the separation driving unit
when the separation driving unit drives the separating unit, and a load
imparting unit, such as a brake plate, which imparts load to the middle
plate, the separating unit, or the like. The brake plate or the like
imparts load when a sheet is separated from the sheet feeding roller by
the separating unit, and the brake plate or the like changes the load to
be imparted, according to the turning angle of the middle plate.

Claims:

1. A sheet feeding apparatus comprising: a feeding unit which abuts on a
sheet and feeds the sheet; a pressure plate having sheets stacked
thereon, and turnably supported so that a sheet on the uppermost layer
among the stacked sheets abuts on the feeding unit; a biasing unit which
biases the pressure plate in order to bring the sheets stacked on the
pressure plate into pressure contact with the feeding unit; a separating
unit which depresses the pressure plate against the biasing force of the
biasing unit and separates the sheet from the feeding unit by a
predetermined distance; a separation driving unit which drives the
separating unit; a measuring unit which measures the driving load applied
to the separation driving unit when the separation driving unit drives
the separating unit; and a load imparting unit which imparts load to at
least any one of the pressure plate, the separating unit, and the
separation driving unit, wherein the load imparting unit imparts load
when the sheet is separated from the feeding unit by the separating unit,
and the load imparting unit changes the load to be imparted, according to
the turning angle of the pressure plate.

2. The sheet feeding apparatus according to claim 1, wherein a first
driving amount of the separation driving unit until the load measured by
the measuring unit exceeds a predetermined threshold value is calculated,
a second driving amount of the separation driving unit until the load
according to the turning angle of the pressure plate when the paper
sheets are fully stacked exceeds the threshold value is calculated, a
third driving amount of the separation driving unit until the load
according to the turning angle of the pressure plate when one sheet is
stacked exceeds the threshold value is calculated, and the stacked amount
of the sheets is calculated by comparing the first driving amount with
the second driving amount and the third driving amount.

3. The sheet feeding apparatus according to claim 1, wherein the
separation driving unit includes a DC motor, and the measuring unit
calculates the driving load applied to the separation driving unit from
the PWM duty at the time of the driving of the DC motor.

4. A sheet feeding apparatus comprising: a feeding unit which abuts on a
sheet and feeds the sheet; a pressure plate having sheets stacked
thereon; a biasing unit which biases the pressure plate in order to bring
the sheets stacked on the pressure plate into pressure contact with the
feeding unit; a separating unit which depresses the pressure plate
against the biasing force of the biasing unit and separates the sheet
from the feeding unit by a predetermined distance; a separation driving
unit which drives the separating unit; and a load imparting unit which
imparts load to at least any one of the pressure plate, the separating
unit, and the separation driving unit, wherein the load imparting unit
imparts load when the sheet is separated from the feeding unit by the
separating unit, and the load imparting unit imparts load when the
distance between the pressure plate and the feeding unit is greater than
a predetermined distance.

5. The sheet feeding apparatus according to claim 4, wherein the
information on the amount of the sheets stacked on the pressure plate is
issued according to the driving amount of the separation driving unit
until the load imparted by the load imparting unit exceeds a
predetermined threshold value after the separation driving unit starts
driving.

6. The sheet feeding apparatus according to claim 5, wherein the
information on a first residual amount is issued when the driving amount
of the separation driving unit until the load imparted by the load
imparting unit exceeds a predetermined threshold value after the
separation driving unit starts driving, and the information on a second
residual amount is issued when the driving amount is within a second
range.

7. The sheet feeding apparatus according to claim 6, further comprising a
display portion which displays the information on the residual amount of
the sheets.

8. An image forming apparatus comprising the sheet feeding apparatus
according to claim 4 and image forming unit which forms an image on a
sheet fed by the sheet feeding apparatus.

Description:

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a sheet feeding apparatus which
has sheets, such as a plurality of sheets of paper, stacked thereon, and
supplies the sheets one by one to a main body of the device.

[0003] 2. Description of the Related Art

[0004] Conventionally, in image forming apparatuses, such as a printer, a
copying machine, and a facsimile, which perform separation and feeding
for a plurality of stacked sheets and form an image on a sheet, there is
a device which detects the stacked amount of sheets as described in
Japanese Patent Application Laid-Open No. H03-079537. In this device, a
message is issued or processing is changed depending on the stacked
amount of sheets detected.

[0005] Additionally, in a sheet feeding device which has sheets stacked on
a pressure plate, moves the pressure plate up and down during sheet
feeding, and makes a feed roller abut on the upper face of a paper,
thereby performing feeding, there is a device as described in Japanese
Patent Application Laid-Open No. 2006-137564 for the purpose of
preventing changes in the operating amount of the pressure plate
depending on the stacked amount of sheets.

[0006] In the device disclosed in Japanese Patent Application Laid-Open
No. 2006-137564, it is possible to keep constant the distance between a
sheet upper face and a feed roller during sheet separation irrespective
of an amount of stacked sheets, and keep constant the operating amount of
the pressure plate during sheet feeding, thereby keeping the timing of
sheet conveyance constant. Also, since it is also possible to minimize
the influence of the stacked sheets on alignment caused by the operation
of the pressure plate, it is possible to perform stable sheet feeding.

[0007] However, when a dedicated switch, a dedicated sensor, and the like
are provided for the detection of the amount of stacked sheets as
described in Japanese Patent Application Laid-Open No. H03-079537, space
and costs will be required mechanistically and electrically.

[0008] Additionally, in Japanese Patent Application Laid-Open No.
H08-259039, a device which detects the stacked amount of sheets without a
dedicated sensor by utilizing an existing sensor for detection of sheet
conveyance is proposed.

[0009] However, since a change in the operating time of the pressure plate
caused by the difference of the stacked amount is detected in Japanese
Patent Application Laid-Open No. H03-079537, it is necessary for the
operating time of the pressure plate to change according to an amount of
stacked sheets.

[0010] Meanwhile, in the sheet feeding device in which the operating
amount of the pressure plate is kept constant for stability of sheet
feeding performance or shortening of time in Japanese Patent Application
Laid-Open No. 2006-137564, the operating time of the pressure plate is
constant irrespective of a stacked amount. Therefore, it is difficult to
apply the technique disclosed in Japanese Patent Application Laid-Open
No. H03-079537.

SUMMARY OF THE INVENTION

[0011] Thus, the object of the invention is to provide a feeder capable of
detecting the stacked amount of sheets without adding a dedicated sensor
or the like, in the feeder which keeps constant the operating amount of a
pressure plate and stabilizes the feed performance of sheets.

[0012] In order to solve the above problems, the invention provides a
sheet feeding apparatus including a feeding unit which abuts on a sheet
and feeds the sheet; a pressure plate having sheets stacked thereon, and
turnably supported so that a sheet on the uppermost layer among the
stacked sheets abut on the feeding unit; a biasing unit which biases the
pressure plate in order to bring the sheets stacked on the pressure plate
into pressure contact with the feeding unit; a separating unit which
depresses the pressure plate against the biasing force of the biasing
unit and separates the sheet from the feeding unit by a predetermined
distance; a separation driving unit which drives the separating unit; a
measuring unit which measures the driving load applied to the separation
driving unit when the separation driving unit drives the separating unit;
and a load imparting unit which imparts load to at least any one of the
pressure plate, the separating unit, and the separation driving unit.
Moreover, the load imparting unit imparts load when the sheet is
separated from the feeding unit by the separating unit, and the load
imparting unit changes the load to be imparted, according to the turning
angle of the pressure plate.

[0013] According to the invention, it is possible to change the load of
the separating operation of separating a sheet on the pressure plate from
the feeding unit according to the turning angle of the pressure plate,
thereby measuring a difference in driving load according to the angle of
the pressure plate during separating operation, i.e., the stacked amount
of sheets, and calculating the rough stacked amount simply from the
measurement result. Additionally, since it is possible to calculate the
measurement of the driving load from the PWM duty of motor driving, there
is also no necessity of newly providing dedicated measuring unit. For
this reason, it is possible to detect the sheet residual amount with a
simple construction while suppressing a cost increase caused by the
addition of a sensor.

[0014] Further features of the present invention will become apparent from
the following description of exemplary embodiments with reference to the
attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a perspective view illustrating the construction of a
main body of an ink jet printer including a sheet feeding apparatus
according to an embodiment of the invention.

[0016]FIG. 2 is a sectional view of the main body of the ink jet printer
of FIG. 1.

[0019] FIGS. 5A and 5B are explanatory views of the periphery of a
depressing claw of FIGS. 4A, 4B, 4C and 4D.

[0020] FIGS. 6A, 6B, 6C and 6D are explanatory views of the sheet feeding
operation when paper sheets are fully stacked within a cassette of FIG.
3.

[0021] FIGS. 7A, 7B, 7C and 7D are explanatory views of the sheet feeding
operation when paper sheets are stacked at a medium level within the
cassette of FIG. 3.

[0022] FIGS. 8A, 8B, 8C and 8D are explanatory views of the sheet feeding
operation when paper sheets are stacked at a low level within the
cassette of FIG. 3.

[0023]FIG. 9 is a graph of the PWM duty during the sheet feeding
operation in the sheet feeding apparatus according to the present
embodiment.

[0024] FIG. 10 is a control block diagram of the present embodiment.

[0025]FIG. 11 is a flow chart for detection of the stacked amount of the
sheet feeding apparatus according to the present embodiment.

DESCRIPTION OF THE EMBODIMENTS

[0026] An embodiment of a sheet feeding apparatus of the invention will
now be described in detail with reference to the accompanying drawings.
Here, although an ink jet printer to which the sheet feeding apparatus of
the invention is applied will be described as an example, it is also
possible to apply the sheet feeding apparatus of the invention to
apparatuses other than the ink jet printer.

[0027]FIG. 1 is a perspective view illustrating the main internal
configuration of an ink jet printer using the sheet feeding apparatus of
the invention, and FIG. 2 is a sectional view illustrating main portions
of the ink jet printer.

[0028] A main body 1 of the ink jet printer illustrated in FIGS. 1 and 2
includes a recording unit 2 which discharges ink drops to the surface of
a sheet, thereby forming an image, and a sheet feeding apparatus 4 which
separates and feeds recording paper sheets P which are the sheets stacked
within the apparatus one by one. A recording paper P separated and fed
from the sheet feeding apparatus 4 is nipped by conveying rollers 32
arranged on a conveying path 31, and is conveyed to a recording unit 2
arranged on the downstream side of the conveying path.

[0029] A carriage 21 which operates to reciprocate in a direction
orthogonal in a paper conveying direction is disposed at the recording
unit 2, and the carriage 22 holds a head (not illustrated) which
discharges ink to a recording paper sheet and an ink tank 22 which
supplies ink to the head.

[0030] In such an ink jet printer, after the leading end position of a
paper sheet conveyed from a conveying unit 3 is conveyed to a
predetermined position, an ink drop is discharged from the head while the
carriage 21 moves in the direction orthogonal to the recording paper
conveying direction, and the image data for a predetermined line is
recorded on the paper. Thereafter, the paper sheet is conveyed by a
predetermined line and the next image data is recorded. The above
sequence is repeated until the recording data for one sheet ends, and if
the recording for one sheet ends, the paper sheet is ejected to a sheet
ejection tray 23 by a sheet ejection roller 24.

[0031]FIG. 3 is a perspective view of the sheet feeding apparatus 4
related to the invention, and sectional views of the sheet feeding
apparatus are illustrated in FIGS. 4A to 4D. FIGS. 4A and 4D are
sectional views illustrating the profile of a cassette 400, FIG. 4B is a
sectional view illustrating the state of rollers or the like, and FIG. 4c
is a sectional view illustrating a depressing operation of a middle
plate. The sheet feeding apparatus 4 is assembled into the
above-described ink jet printer which is an image forming apparatus, and
is able to feed so-called fixed size sheets, such as A4, letter (LTR),
and legal (LGL).

[0032] First, the construction of the present embodiment will be
described. As illustrated in FIG. 3, a sheet feeding cassette 400, which
is constructed by a box-shaped frame 401 and has an open upper face, is
adapted to be attachable to and detachable from the right of FIG. 2 along
a cassette guide (not illustrated) provided at the main body of the ink
jet printer. A middle plate 402 serving as a pressure plate which has an
end rockably journalled by a pivot 401A is arranged inside the frame 401
of the sheet feeding cassette 400. As illustrated in FIG. 4B, a coil
spring 403 serving as a biasing unit is arranged between the middle plate
402 and the bottom of the frame 401, and the middle plate 402 is biased
in the direction of an arrow X in FIG. 4D by the resilient force of the
coil spring 403.

[0033] A sheet feeding roller shaft 404 supported by the frame of the main
body of the printer is arranged above the end of the middle plate 402
opposite to the pivot 401A. A sheet feeding roller 405 is attached to the
sheet feeding roller shaft 404 as a feeding unit.

[0034] When the middle plate 402 is biased and turned in the direction of
the arrow X by the resilient force of the coil spring 403, a paper P1 on
the uppermost layer among the paper sheets P stacked on the middle plate
402 abuts on the sheet feeding roller 405, and the turning of the middle
plate 402 is stopped, thereby bringing the paper sheet into a feeding
allowable state.

[0035] Additionally, a separation roller 409 is arranged to face the sheet
feeding roller 405, and the separation roller 409 is supported by a
holder 408 which is rockable about a pivot 408A. The holder 408 is biased
toward the sheet feeding roller 405 by a spring (not illustrated), and as
a result, the separation roller 409 and the sheet feeding roller 405
maintain the state of being brought into pressure contact with each
other. The separation roller 409 is supported by the holder 408 via a
torque limiter (not illustrated), and is adapted to rotate with respect
to the holder 408 at a predetermined torque or more. Then, when the sheet
feeding roller 405 is rotationally driven, the paper P stacked on the
middle plate 402 is fed into a nip portion between the sheet feeding
roller 405 and the separation roller 409. In a case where the paper sheet
led to the nip portion is a single sheet, the separation roller 409 is
rotated to follow the paper sheet to be fed. However, in a case where two
sheets of paper are overlappingly fed, the frictional force caused by the
torque limiter surpasses the frictional force between paper sheets, the
rotation of the separation roller 409 is stopped, the lower paper sheet
of the overlapped paper sheets is blocked by the separation roller 409,
and only the paper sheet on the uppermost layer is conveyed to the
downstream.

[0036] Additionally, a return lever 410, which pushes the paper sheets
back to the cassette after a second sheet of paper has been projected to
the downstream from the sheet feeding cassette 400 by the paper feeding
operation, is provided, and the return lever 410 is adapted to be
turnable about the pivot 410A and movable up and down.

[0037] The tip of the return lever 410 is arranged so as to draw a turning
locus such that the tip of the return lever retreats to the outside of a
paper passing path on the downstream side with respect to the nip portion
between the sheet feeding roller 405 and the separation roller 409,
enters the paper passing path in the vicinity of the nip portion, and
retreats to the outside of the paper passing path again on the upstream
side.

[0038] Additionally, a holder release lever 411 is provided to be
engageable with and separable from the holder 408, and is adapted to be
turnable about the pivot 411A. In a case where the holder release lever
411 is at a position where the holder release lever engages with the
holder 408, the holder 408 is turned in a direction in which the holder
is separated from the sheet feeding roller 405 against a spring force,
and consequently, the separation roller 409 is separated from the sheet
feeding roller 405. On the other hand, in a case where the holder release
lever 411 is at a position where the holder release lever is separated
from the holder 408, the holder 408 maintains the pressure contact state
between the sheet feeding roller 405 and the separation roller 409 by a
spring force.

[0039] Cam followers (not illustrated) are respectively provided at the
end of the pivot 410A of the lever 410 and the end of the pivot 411A of
the holder release lever 411. Each cam follower engages with the cam face
of the control cam 412, and the cam face is formed so that the return
lever 410 and the holder 411 perform a desired paper separating operation
according to the rotation of the control cam 412.

[0040] Moreover, an example of a separating unit which constitutes the
sheet feeding apparatus of the invention and a separation driving unit
which moves the separating unit will be described.

[0041] A depressing cam shaft 406 is provided on the upstream side in the
conveying direction of the sheet feeding roller shaft 404, and depressing
cams 407 are attached to the positions where the depressing cams do not
interfere with the recording paper P outside the sheet width of the
recording paper P on the middle plate 402, at both ends of this cam
shaft.

[0042] Additionally, a depressing slider 413 is provided which is adapted
to be movable up and down (the X direction or its opposite direction in
the drawing) with respect to the sheet feeding cassette 400. The
depressing slider 413 is attached so as to be movable up and down as the
depressing slider is attached to and guided by a slide guide 401B
provided in the shape of a vertically long punching hole in the frame
401. An upper portion of the depressing slider 413 is formed with an
upper end projection 413A, and the upper end projection 413A is adapted
to be always brought into sliding contact with the outer peripheral cam
face of the depressing cam 407 as the depressing slider 413 is biased
upward by the coil spring 418. Therefore, as the depressing cam 407
rotates, the depressing slider 413 is rocked in the direction of the
arrow X along the slide guide 401B along the cam profile of the
depressing cam 407.

[0043] Additionally, a depressing claw 414 is provided inside the
depressing slider 413. FIG. 5A is a view illustrating the construction of
the depressing slider 413 and the depressing claw 414. By making a guide
hole 413B provided in the depressing slider 413 engage with a guide shaft
414A of the depressing claw 414, the depressing claw 414 is adapted to be
movable in the direction of an arrow W in the drawing orthogonal to the
rocking direction of the depressing slider 413, or its opposite
direction. On the other hand, a guide shaft 414B is formed at the
depressing claw 414, and engages with a guide hole 401C provided in the
frame 401. The depressing claw 414 is always biased in the W direction by
a spring 415, and the guide shaft 414B of the depressing claw 414 is
positioned as the guide shaft is brought into sliding contact with a cam
face 401D of the guide hole 401C. The end of the depressing claw 414 is
provided with a claw portion 414C of which the tip is formed toward the
movement direction (the W direction), and a middle plate claw 416 is
attached to the tip side of the middle plate 402 so as to face the claw
portion 414C. The middle plate claw 416 is adapted to be slidable with
respect to the middle plate 402, and is biased in a direction in which
the middle plate claw approaches the depressing claw 414 by a spring (not
illustrated).

[0044] Then, as the depressing slider 413 moves up and down, the shaft
414B slides on the cam face 401D, and the depressing claw 414 moves. When
the depressing slider 413 moves up, the depressing claw 414 moves in a
direction (direction opposite to the arrow W in the drawing) in which the
depressing claw is separated from the middle plate claw 416 against the
resilient force of the spring 415. On the other hand, when the depressing
slider 413 rocks downward, the claw portion 414C of the depressing claw
414 moves so as to engage with the middle plate claw 416 by the resilient
force of the spring 415, and the engaged middle plate claw 416 is
depressed to rock the middle plate 402 by a predetermined amount in the
direction opposite to the arrow X. In addition, when the claw portion
414C of the depressing claw 414 engages with the middle plate claw 416,
the depressing claw 414 pushes the middle plate claw 416 in a sliding
direction (W direction in the drawing) against the biasing force of the
spring 417, and the middle plate claw 416 slides to a position where the
middle plate claw butts against a butting portion (not illustrated) of
the middle plate 402.

[0045]FIG. 5B is a view illustrating the periphery of the depressing claw
414 and the middle plate claw 416. As illustrated in FIGS. 5A and 5B, the
claw portion 414C of the depressing claw 414 includes a locking face 414D
and a tapered face 414E, respectively, and a claw portion 416A of the
middle plate claw 416 also includes a locking face 416B and a tapered
face 416C, respectively.

[0046] When the middle plate 402 is intended to rock in the direction
opposite to the arrow X, since the tapered face 414E of the depressing
claw 414 and the tapered face 416C of the middle plate claw 416 engage
with each other, the depressing claw 414 escapes in the direction
opposite to the arrow W, and the middle plate 402 is rockable without
being regulated in movement. Additionally, when the middle plate 402 is
intended to rock in the direction of the arrow X, the locking face 414D
of the depressing claw 414 and the locking face 416B of the middle plate
claw 416 engage with each other, the depressing claw 414 is not able to
move in the direction opposite to the arrow W, and the rocking of the
middle plate 402 is regulated. In this way, the claw portion 414C of the
depressing claw 414 and the claw portion 416A of the middle plate claw
416 constitute a ratchet mechanism in which movement in one direction is
regulated and movement in the other direction is free.

[0047] Additionally, the sheet feeding roller 405, the depressing cam 407,
and the control cam 412 (FIG. 3) are rotationally driven by receiving the
driving from a sheet feeding motor 324 (FIG. 10), which is a driving
source connected through gears.

[0048] In addition, the sheet feeding cassette 400 is provided with a
middle plate locking mechanism (not illustrated) for locking the middle
plate 402 at a depressed position when the middle plate 402 is depressed
downward in a state where the sheet feeding cassette is pulled out of the
main body 1 of the ink jet printer. Thereby, it is possible to secure a
wide stacking space for the paper P, thereby easily setting the paper P
on the middle plate 402. Then, when the sheet feeding cassette 400 is
mounted on the main body 1 of the ink jet printer in a state where the
middle plate 402 is locked by the middle plate locking mechanism, the
locking of the middle plate 402 by the middle plate locking mechanism is
released by a middle plate unlocking portion (not illustrated) formed in
the cassette guide during the mounting.

[0049] Next, a series of sheet feeding operations in the sheet feeding
apparatus 4 which is a first embodiment will be described with reference
to FIGS. 6A to 8D. FIGS. 6A to 6D show a case (when paper sheets are
fully stacked) where the stacked amount of paper sheets stacked on the
middle plate 402 is large, FIGS. 7A to 7D show a case (when stacked at a
medium level) where the stacked amount of paper sheets is about the half,
and FIGS. 8A to 8D show a case (when stacked at a low level) where the
stacked amount of paper sheets is small.

[0050] When the middle plate 402 is depressed in a state where the sheet
feeding cassette 400 is pulled out of the main body 1 of the ink jet
printer, the middle plate 402 is locked by the middle plate locking
mechanism (not illustrated), and a bundle of paper sheets is set on the
middle plate 402 in that state. Next, when the sheet feeding cassette 400
is mounted on the main body 1 of the ink jet printer, the locking of the
middle plate locking mechanism is released by the middle plate unlocking
portion. At this time, the depressing slider 413 attached to the sheet
feeding cassette 400 is mounted in a state where the depressing slider
has abutted on the depressing cam 407 attached to the depressing cam
shaft 406.

[0051] As illustrated in FIGS. 6A, 7A, and 8A, when the sheet feeding
cassette 400 is mounted to a predetermined position, the upper end
projection 413A provided on the depressing slider 413 engages with a
recess 407A of the depressing cam 407, which leads to a standby state. In
this state, the claw portion 414C of the depressing claw 414 engages with
the claw portion 416A of the middle plate claw 416, and the upper face of
the stacked paper sheets P and the sheet feeding roller 405 are separated
from each other. Additionally, the separation roller 409 is brought into
pressure contact with the sheet feeding roller 405, and the return lever
410 is on the upstream side of the separation roller, i.e., at a position
where a paper sheet is prevented from entering the nip portion between
the sheet feeding roller 405 and the separation roller 409.

[0052] When the sheet feeding motor 324 which is a driving source (not
illustrated) begins to rotate on the basis of a sheet feeding signal, the
sheet feeding roller 405, the depressing cam 407, and the control cam 412
rotate via a gear train. As indicated by arrows in the drawings, the
sheet feeding roller 405 rotates clockwise, and the depressing cam 407
and the control cam 412 rotate counterclockwise. Since the depressing
slider 413 is biased upward by the resilient force of the coil spring 418
and the upper end projection 413A always abuts on the depressing cam 407,
the upper end projection 413A moves along the profile of the depressing
cam 407. Thereby, the depressing slider 413 rocks upward along the slide
guide 401B, and the depressing claw 414 attached to the depressing slider
413 also rocks upward similarly to the depressing slider 413. At this
time, the return lever 410 moves to a retreat position out of the paper
passing path on the downstream side of the separation roller as the cam
follower which engages with the cam face of the control cam 412 turns
along the cam face.

[0053] When the sheet feeding roller 405 is further rotated, the
depressing slider 413 rocks further upward. Then, the shaft 414B of the
depressing claw 414 slides on the cam face 401D of the frame 401, and the
depressing claw 414 moves substantially horizontally in the direction
opposite to the arrow W inside the depressing slider 413 along the cam
face 401D. Thereby, the depressing claw 414, and the middle plate claw
416 attached to the middle plate 402 are disengaged from each other, and
the regulation of the middle plate 402 is released. Since the middle
plate 402 is always biased upward by the coil spring 403, when the
regulation is released, the middle plate 402 ascends in the direction of
the arrow X about the pivot 401A. Then, the uppermost paper P1 stacked on
the middle plate 402 is brought into pressure contact with the sheet
feeding roller 405 (FIGS. 6B, 7B, and 8B). As the sheet feeding roller
405 rotates further, the paper P1 is fed in the direction of an arrow Y
in the drawings due to the friction between the sheet feeding roller 405
and the uppermost paper P1.

[0054] When the delivered paper sheet reaches a position between the sheet
feeding roller 405 and the separation roller 409, the paper sheet is
separated one by one as described above at the nip portion. The
depressing cam 407 rotates further and begins to depress the upper end
projection 413A of the depressing slider 413. The depressing slider 413
moves downward along the guide 401B formed on the sheet feeding cassette
400 against the resilient force of the spring 418. When the depressing
slider 413 rocks downward, the depressing claw 414 moves in the direction
of the arrow W within the depressing slider 413 by the coil spring 415
while the guide shaft 414B is brought into sliding contact with the cam
face 401D (FIG. 5A).

[0055] Then, the depressing claw 414, and the middle plate claw 416
attached to the middle plate 402 begin to engage with each other (FIGS.
6C, 7C, and 8C). When the rotation of the depressing cam 407 proceeds
further, the locking face 414D (FIG. 5B) of the depressing claw 414 and
the locking face 416B (FIG. 5B) of the middle plate claw 416 engage with
each other. Moreover, with the descent of the claw portion 414C of the
depressing claw 414, the middle plate claw 416 also descends and the
middle plate 402 is depressed (FIGS. 6D, 7D, and 8D).

[0056] By rocking the depressing slider 413 downward by the depressing cam
407 in this way, the middle plate claw 416 is depressed. Thereby, the
middle plate 402 is rocked in the direction opposite to the arrow X
against the resilient force of the coil spring 403, and a predetermined
separation distance is created between the sheet feeding roller 405 and
the uppermost face of the paper sheet with a predetermined gap distance
left between the upper face of the uppermost paper P1 on the middle plate
402, and the sheet feeding roller 405. In that case, the above return
lever 410 moves to the nip portion between the sheet feeding roller 405
and the separation roller 409 while the cam follower (not illustrated)
turns along the cam face of the control cam 412, and enters a paper
conveying path. Simultaneously, the cam follower (not illustrated) turns
along the cam face of the control cam 412, and the holder release lever
411 separates the separation roller 409 journalled to the holder 408 from
the sheet feeding roller 405. After the separation roller 409 is
separated from the sheet feeding roller 405, the cam follower (not
illustrated) turns further along the cam face of the control cam 412, and
the return lever 410 retreats to the outside of the conveying path on the
upstream side of the separation roller 409.

[0057] Through the series of movements of the return lever 410 described
above, the paper sheets after a second sheet of paper blocked by the nip
portion between the sheet feeding roller 405 and the separation roller
409 are pushed back to the inside of the sheet feeding cassette by the
tip of the return claw 410. Thereafter, the cam follower (not
illustrated) turns further along the cam face of the control cam 412 of
the holder release lever 411. The separation roller 409 journalled to the
holder 408 is brought into pressure contact with the sheet feeding roller
405 again, and conveys one separated recording paper sheet while nipping
the paper sheet by the nip portion between the separation roller and the
sheet feeding roller 405. In this way, the operation of separating and
feeding one paper from the paper sheets stacked within the sheet feeding
cassette 400 is reliably performed.

[0058] Thereafter, when the sheet feeding roller 405 is further rotated,
as illustrated in FIGS. 6A, 7A, and 8A, the upper end projection 413A
provided on the depressing slider 413, and the recess 407A of the
depressing cam 407 engage with each other. The sheet feeding roller 405
is held at an initial standby position (home position) by the engagement
between the upper end projection 413A and the recess 407A, and a series
of separating operations ends. A series of operations until a
predetermined separation distance is created between the upper face of
the paper sheets P and the sheet feeding roller 405 and returning to the
standby position is made from the start of engagement between the
depressing claw 414 and the middle plate claw 416 described above is
hereinafter referred to as "predetermined distance separating operation".

[0059] Then, the uppermost paper P1 is nipped by the sheet feeding roller
405 and the separation roller 409, and is separated and conveyed toward a
pair of conveying rollers 32 provided on the downstream side, and the
paper sheet is further conveyed to the recording unit 2 by the pair of
conveying rollers 32. Then, when the sheet feeding roller 405 is
subsequently rotated, it is possible to feed the following paper sheets P
continuously similarly to the above.

[0060] Additionally, in the present embodiment, a brake plate 420 is
provided at a position corresponding to the middle plate claw 416 below
the tip side of the cassette frame 401 in the feed direction. The brake
plate 420 is biased in the direction of the middle plate claw 416 by the
spring 421. The brake plate 420 is arranged so as to be brought into
pressure contact with and slide on a sliding portion 416D provided at the
tip of the middle plate claw 416 during the descent (Refer to FIGS. 6D,
7D, and 8D) when the middle plate claw 416 descends according to the
turning of the middle plate 402 in a state where the middle plate claw
416 is pushed by the depressing claw 414 and is pushed out in the feed
direction. In addition, one of the sliding portion 416D of the middle
plate claw 416 and the brake plate 420 is made of a rubber material (for
example, silicon rubber) with a high sliding resistance.

[0061] Since the brake plate 420 is provided below the frame 401, only
when the tip of the middle plate 402 turns to below the frame 401 and the
middle plate claw 416 is moved further in the direction of the brake
plate 420, the brake plate 420 and the sliding portion 416D are brought
into pressure contact with and slide on each other. That is, the brake
plate and the sliding portion are brought into pressure contact with and
slides on each other during the predetermined distance separating
operation. The function of the brake plate 420 will be described later.

[0062] In the ascent/descent operation of the middle plate 402 described
above, as illustrated in FIGS. 6A to 8D, even if the stacked amount
(stacked height) of the paper sheets P stacked on the middle plate 402
becomes different, the position where a plurality of claw portions 414C
provided at the depressing claw 414 and the claw portion 416A of the
middle plate claw 416 engage with each other varies. Thereby, the middle
plate 402 is separated from the sheet feeding roller 405 with almost the
same timing as the start of rotation of the sheet feeding roller 405.
Moreover, it is possible to perform a predetermined separation distance
between the uppermost face of the paper sheets P stacked and the sheet
feeding roller 405. By separating the sheet feeding roller 405 and the
paper sheet from each other by a predetermined distance, the time until a
sheet is brought into pressure contact with the sheet feeding roller 405
from the start of sheet feeding becomes uniform, and it is consequently
possible to keep the sheet feeding operating time constant. Additionally,
by separating a paper sheet at a position near the sheet feeding roller
405 and making the paper stand by, there are advantages that it is
possible to prevent the middle plate 402 from ascending vigorously, and
it is possible to reduce the collision sound between the paper sheet and
the sheet feeding roller 405 generated during paper feeding.

[0063] FIG. 10 is a control block diagram of the present embodiment. In
FIG. 10, a control unit 300 which is control unit includes a CPU 310, a
ROM 311 which stores a program or fixed data, and a RAM 312 provided with
a region where image data is developed, a working region, and the like.

[0064] A conveying motor which drives the conveying roller and the sheet
ejection roller 24 is designated by 321, a carriage motor which moves the
carriage 22 for scanning is designated by 322, and a recording head is
designated by 323. Additionally, the control unit 300 also includes a
driver for driving the various above-described motors and recording head
1. A sheet feeding motor which drives the sheet feeding roller 405 is
designated by 324. The sheet feeding motor 324 also drives the depressing
cam 407 and the control cam 412.

[0065] As for the sheet feeding motor 324, a DC motor is used as a motor
for the driving of the sheet feeding apparatus. Also, a PWM (pulse width
modulation) control is used as a driving control method of the DC motor.
Additionally, a system is adapted so that a driving system is provided
with an encoder 325 and the driving amount and driving speed of a driving
system at a point of time of the output of the encoder 325 is capable of
being calculated from the output of the encoder 325. The driving of the
driving system of the sheet feeding apparatus related to the present
embodiment is controlled by the feedback control of modulating (changing
duty) the pulse width of an electric current to be applied to the DC
motor on the basis of driving information, including driving amount,
driving speed, and the like, and making the above driving amount and
driving speed reach a targeted driving amount and driving speed. Here, if
the pulse width is made large (the duty is made large), the motor output
becomes large, and if pulse width is made small (the duty is made small),
the motor output becomes small. That is, a control is made so that the
duty of PWM is raised in order to raise the motor output in a case where
the load applied to the driving system during motor driving has been
increased, and the duty of PWM is lowered in order to suppress the motor
output in a case where the load has been reduced.

[0066]FIG. 9 is a typical graph illustrating changes in PWM duty during
individual sheet feeding operations when the paper stacked amount of the
sheet feeding cassette 400 is full, medium, and small. The horizontal
axis represents the time from the start of the feeding of one paper sheet
to the end of the feeding thereof. Additionally, the vertical axis
represents PWM duty. A solid line indicates the PWM duty when paper
sheets are fully stacked, a one-dot chain line indicates the PWM duty
when paper sheets are stacked to a medium level, and a dotted line
indicates the PWM duty when paper sheets are stacked to a low level. When
sheet feeding is started, the PWM duty increases and decreases according
to the magnitude of the loads applied to the driving system in the series
of sheet feeding operations described above, such as the retreat
operation of the return lever 410, the disengagement between the
depressing claw 414 and the middle plate claw 416, the pressure contact
between the sheet feeding roller 405 and the paper sheets, and the single
sheet paper separating operation.

[0067] In the predetermined distance separation operation when the paper
stacked amount within the cassette 400 is full, as illustrated in FIGS.
6D and 6A, the sliding portion 416D and the brake plate 420 maintain a
contact state when the sliding portion 416D of the middle plate claw 416
moves downward during sheet feeding operation. In the predetermined
distance separation operation when the paper stacked amount within the
cassette 400 is medium, as illustrated in FIGS. 7D and 7A, the sliding
portion 416D of the middle plate claw 416 comes into contact with the
brake plate 420 similarly to when paper sheets are fully stacked.
However, as illustrated in FIG. 7c, the sliding portion 416D has not yet
descended to the same height as the brake plate 420 when the middle plate
claw 416 and the depressing claw 414 begin to engage with each other.
Therefore, the time at which the sliding portion 416D and the brake plate
420 begin to come into contact with each other will be later than when
paper sheets are fully stacked.

[0068] Moreover, in a case where the paper stacked amount within the
cassette 400 is small, as illustrated in FIGS. 8D and 8A, the sliding
portion 416D and the brake plate 420 begin to come into contact with each
other even later than when paper sheets are stacked to a medium level.

[0069] For this reason, in the predetermined distance separation operation
in the sheet feeding operation, when paper sheets are fully stacked, the
load torque caused by the brake plate 420 is added to the load torque of
the driving system, the load torque increases at the beginning of the
predetermined distance separation operation, and after this, the
increased state is maintained until the time of sheet feeding standby.
Additionally, the timing with which the load torque increases is
gradually delayed as the paper stacked amount decreases. That is, when
the uppermost face of the stacked paper sheets P is a predetermined
separation distance from the sheet feeding roller 405, the brake plate
420 or the like becomes a load imparting unit which imparts load, and
changes the load according to the turning angle of the middle plate
(pressure plate).

[0070] Concerning operations other than the predetermined separation
distance, the pressure contact force between the sheet feeding roller 405
and the paper sheets, the pressure contact force between the separation
roller 409 and the sheet feeding roller 405, the turning torque of the
return lever 410 and the holder release lever 411, and the like are
uniformly set irrespective of the amount of stacked paper sheets within
the cassette 400. For this reason, the variation of the motor load torque
of the sheet feeding operation has different load torque variation curves
during the predetermined distance separation operation, and has the same
variation curve irrespective of a stacked amount when not in the
predetermined distance separation operation. That is, the variation curve
of the PWM duty of a motor during the sheet feeding operation has
different variations during the predetermined distance separation
operation (the range of A in FIG. 9), and has the same variation
irrespective of a stacked amount when not in the predetermined distance
separation operation (the range of A in FIG. 9). If the difference of
this PWM duty variation curve is detected by a measuring unit, it is
possible to detect an approximate paper stacked amount within the
cassette 400.

[0071]FIG. 11 is a control flow chart of detection of the paper stacked
amount within the cassette 400 and an apparatus display portion. H is a
threshold value for determining whether or not the PWM duty meets the
above-described increase curve. C is the motor driving amount from the
start of sheet feeding when the PWM duty exceeds a threshold value H (a
first driving amount). The motor driving amount (second driving amount)
when the PWM duty exceeds the threshold value H when paper sheets are
fully stacked is defined as C1, and the driving amount (third driving
amount) when the PWM duty of the last paper sheet exceeds the threshold
value H (when the last paper sheet is stacked) is defined as C2. In the
following calculation formula, it is possible to roughly calculate the
stacked paper residual amount ratio R within the cassette.

Stacked paper residual amount ratio R(%)=(C2-C)/(C2-C1)×100.

[0072] Hereinafter, the details of the flow chart will be described with
reference to FIG. 11. If a printing command is issued, driving of the
sheet feeding motor is started, and simultaneously, counting of the
driving amount of the motor is started (Step S501). Next, the value of
the PWM duty of the sheet feeding motor is compared with the threshold
value H (Step S502), and the driving amount C at that time is stored when
the value of PWM exceeds H (Step S503). The stacked paper residual amount
ratio R within the cassette is calculated according to the
above-described calculation formula (Step S504). The stacked paper
residual amount ratio R is displayed on the display portion (Step S505).
Moreover, if 10<R≦50, a message which urges preparation of
paper sheets is displayed on the display portion (Step S506), and if R10,
a message which provides notification that paper sheets will soon run out
is displayed (Step S507).

[0073] By such a display operation, an operator is able to know the rough
residual amount of paper sheets in advance and prepare for supply of
paper sheets, and it is possible to avoid trouble problem in which paper
sheets run out suddenly, printing cannot be performed, and stalling
occurs.

[0074] In the present embodiment, although two-step state transition of
50% and 10% as residual amounts is used, it is also possible to perform
guide display according to a residual amount in detail for an operator
through further finer divisions.

[0075] Additionally, it is also possible to provide an indicator portion
using scales or the like on the display portion 326, and indicate a
change in the above residual amount ratio R so as to know the change
visually.

[0076] Accordingly, according to the invention, it is possible to detect
the paper residual amount within the cassette without adding a new sensor
for detecting paper stacked amount, and it is also possible to construct
the invention easily without necessitating complicated mechanisms. For
this reason, costs can also be suppressed.

[0077] In the above embodiment, the stacked paper residual amount ratio R
is calculated using the driving amount C. However, the information of the
residual amount may be issued simply according to the driving amount C,
and may be displayed on the display portion 236. For example, when the
driving amount C is within a first range between C1 and C2 of FIG. 9, the
paper residual amount is displayed to be a first residual amount (for
example, 50% of residual amount), and when the driving amount is within a
second range greater than C2, the paper residual amount is displayed to
be a second residual amount (10% of residual amount).

[0078] While the present invention has been described with reference to
exemplary embodiments, it is to be understood that the invention is not
limited to the disclosed exemplary embodiments. The scope of the
following claims is to be accorded the broadest interpretation so as to
encompass all such modifications and equivalent structures and functions.

[0079] This application claims the benefit of Japanese Patent Application
No. 2009-282696, filed Dec. 14, 2009 which is hereby incorporated by
reference herein in its entirety.

Patent applications by Kazuyuki Morinaga, Machida-Shi JP

Patent applications by Kenji Kawazoe, Yokohama-Shi JP

Patent applications by Masaya Shimmachi, Kawasaki-Shi JP

Patent applications by Tetsu Hamano, Tokyo JP

Patent applications by Toshiaki Tokisawa, Yokohama-Shi JP

Patent applications by CANON KABUSHIKI KAISHA

Patent applications in class By means to convey sheet (e.g., from pack to operation)

Patent applications in all subclasses By means to convey sheet (e.g., from pack to operation)